The present invention relates to U.S. Pat. No. 3,641,408 and to the corresponding Reissue Patent No. 28,618 entitled "SOLID-STATE POWER SUPPLY SYSTEM FOR ROTATING ANODE X-RAY TUBES," issued to Louis L. Fiocca and assigned to the same assignee as the present invention. Louis L. Fiocca, the inventor of the system of Reissue Patent No. 26,618 is also the inventor of the present invention and Mr. Fiocca's continuing work with the system disclosed in the Reissue Patent No. 28,618 resulted in the improvement comprising the present invention.
As will be appreciated, the present invention utilizes a similar concept, and much of the circuitry disclosed is the system of the Reissue Patent No. 28,618 and, in fact, the present invention eliminates a significant portion of the circuitry of the system disclosed in the Reissue Patent No. 28,618 while providing an improved operating result. Accordingly, for the purpose of simplification of the description of the circuitry in this application, reference as appropriate is made to said Reissue Patent No. 28,618 for the details of the circuitry shown and described therein.
X-ray tubes having rotatable anodes are well known. In such tubes, the anode is caused to rotate to present a continually changing target area so that heat generated by the X-ray bombardment may be more easily dissipated. This heat dissipation enables higher energy levels to be used resulting in increased X-ray output as compared with tubes having fixed anodes.
The rotating anodes of X-ray tubes are generally driven with split phase motors and in fact may be the rotors of said motors. The motors have been heretofore operated from power sources capable of providing either 60 Hz or 180 Hz A.C. control power to enable anode rotation at a first relatively low speed and at a second relatively high speed. Such prior art systems require means to accelerate from a quiescent condition to attain the final operating speed for the X-ray anode in the desired operating running mode.
The rotating anode and the motor drive generally exhibit mechanical resonances at the speed in the range of 4,000 to 6,000 and RPM and it is desirable to make the transistion through such resonances both on acceleration and deceleration of the anode as briefly as possible to minimize bearing wear of the anode system and to minimize undue strain on the bearing mounts and the tube structure.
In the prior art, X-ray tube starter systems, such as shown in the Reissue Patent No. 28,618, a first starter or drive system has been utilized to drive the rotor up to its slow speed operating condition and a second starter has been utilized to drive the rotor to its high speed operating condition. Two essentially separate starting systems are employed, and the systems operate in generally digital or discrete fashion.
In contrast to the prior art, the present starter and drive system operate in an analog manner and can be controlled to accelerate or boost the rotor to a first selected running speed, and can also be controlled to accelerate and boost the rotor to a second selected running speed, and either of the selected running speeds can be varied within a given operating range.
The well known principle of phase control of SCR's (silicon controlled rectifiers) described and utilized in Reissue Patent No. 28,618 is also utilized and applied in the present invention.
Briefly, and as is well known, an SCR which is gated or triggered to conduction, will conduct for the remainder of a half cycle of the A.C. (alternating current) wave provided to its anode - cathode current path. Thus, dependent on the point at which the SCR is triggered to conduction, relative to the phase angle of the applied A.C. wave, the SCR will conduct current for a selected controllable time period.
Consider briefly an application of the present invention. An X-ray examination will conventionally have at least two X-ray tubes; one of the tubes is normally for doing fluoroscopic examinations and is referred to as "undertable tube," and the other tube is normally used for doing radiographic exposures and is commonly referred to as the "overtable tube". For doing fluoroscopic examinations, the undertable tube is operated at a relatively low speed such as at 100 RPM and therefore, this tube requires a low speed starter to boost the rotating speed of the rotor to a desired relatively low rotating speed. In contrast, radiographic exposures are preferably done at high speeds, say at 10,000 RPM, and therefore the overtable tube requires a high speed starter to boost rotating speed of the rotor to a relatively high running speed. The present invention provides a single starter and drive means for accelerating and operating both of the aforesaid tubes at the required operating speeds.
As discussed above, the circuitry in the present application is similar to that of the Reissue Patent No. 28,618 with the improvement that the 60 Hz phase shift network block 20, the 60 Hz SCR bridge 21 and the 24 VDC logic power supply 11 coupled to block 20, and the two second timer 26 are removed from the system of the present invention. In addition to eliminating components and circuitry and reducing costs, the present circuitry provides improved operating results over the circuit disclosed in U.S. Pat. No. 3,641,408, as will be explained.
As also mentioned hereinabove, since the circuitry of the present invention is in considerable part the same as that described in the Reissue Patent No. 28,618, reference is specifically made to that patent as needed to clarify the description of the present invention. And the reference numerals referring to the blocks in the FIGURE of the present invention refer to the similarly numbered blocks in FIG. 1 of the Reissue Patent No. 28,618.